In the past, various types of disposable and reusable thermal ink jet pens have been developed for use in thermal ink jet printers. Examples of such disposable pens may be found in U.S. Pat. No. 4,771,295, issued to Jeffrey P. Baker et al. in U.S. Pat. No. 4,931,811, issued to Bruce Cowger et al., in U.S. Pat. No. 4,791,438 issued to Gary E. Hanson et al., and in U.S. Pat. No. 4,831,389 issued to C. S. Chan. All of these patents are assigned to the present assignee and are incorporated herein by reference.
More recently, there has been developed a refillable ink cartridge which has certain ink-independent advantages over the earlier disposable thermal ink jet pens of the types described in the above Hewlett Packard-assigned patents. This refillable thermal ink jet pen and these ink-independent advantages over earlier art are disclosed and claimed in co-pending applications entitled "Ink Pressure Regulator For A Thermal Ink-Jet Printer" Ser. No. 07/928,811, filed Aug. 12, 1992, by Tofigh Khodapanah et al, and "Collapsible Ink Reservoir Structure and Printer Ink Cartridge", Ser. No. 07/929,615, filed Aug. 12, 1992, by George T. Kaplinsky et al. These co-pending applications are also assigned to the present assignee and are also incorporated herein by reference.
The above Kaplinsky pen utilizes an ink pressure regulator within a flexible ink bag reservoir for a replaceable or refillable ink cartridge. This ink pressure regulator comprises a bow spring configured to have substantially linear force/deflection characteristics and a pair of adjacent plates which collapse to a substantially flat shape to minimize the amount of ink remaining within the ink bag reservoir after thermal ink jet printing has substantially depleted the ink from the ink cartridge.
All of the above identified Hewlett Packard inventions represent most significant advances in the art and technology of thermal ink jet printing.